Work is in progress to develop procedures for long-term preservation by freezing of transplantable organs which require perfusion by blood for resuscitation and prolonged survival following reimplantation. A thermally controlled liquid perfusion system that has the capacity to control a number of parameters, including perfusate composition, flow, pressure, cycling, oxygenation, sterility, and temperature is being employed in these studies. Turtle hearts are preserved at minus 6 degrees Centigrade in frog Ringer's solution containing 2.56 M DMSO. The heart is perfused at 25 degrees Centigrade via the vascular system for a 30 minute period while DMSO is added incrementally until a final perfusate concentration of 2.56 M DMSO is reached. The heart is then transferred to a minus 6 degrees Centigrade freezer for storage. Viability is established by the degree of resumption of spontaneous myocardial activity. Rabbit kidneys will be subjected to non-aqueous perfusates such as vegetable oil containing DMSO prior to the freeze-thaw cycle. Kidney viability and functional integrity is measured using: (1) vascular resistance and flow, (2) silicone rubber vascular injection procedures, (3) microscopic tissue sections, (4) autograft or replantation of the preserved organ.